# Antimicrobial Activity of Bioactive Peptides on Resistant Enterobacteriaceae and the Viability of Giardia duodenalis Cysts Isolated from Healthy Dogs

## TL;DR

This study shows that certain natural peptides can effectively kill drug-resistant bacteria and a parasite in dogs, offering new treatment possibilities.

## Contribution

The study demonstrates the in vitro antimicrobial activity of temporins against resistant Enterobacteriaceae and Giardia duodenalis in dogs.

## Key findings

- Three peptides inhibited the growth of Enterobacter strains in a concentration-dependent manner.
- Four peptides completely prevented the survival of Giardia duodenalis cysts at higher concentrations.
- The results suggest that antimicrobial peptides could be a promising alternative for treating resistant infections in dogs.

## Abstract

Dogs can carry microorganisms that may cause illness in animals and people, including certain bacteria and intestinal protozoa. Some of these microorganisms are becoming difficult to treat because they no longer respond well to common drugs. For this reason, new ways to control infections must be sought urgently. In this study, we examined whether small natural-like peptides called temporins could reduce or stop the growth of these germs. We collected samples from fifty dogs and selected the samples positive for Enterobacter strains and the intestinal protozoon (Giardia). We exposed the bacteria and the parasite to six different peptides. Three of these peptides inhibited the growth of the bacteria, while four were able to completely prevent the survival of the Giardia parasite, although their effectiveness depended on how much of the peptide was used. These findings suggest that certain peptide molecules may offer new options for controlling infections in dogs, especially at a time when resistance to current medicines is increasing. Further research may help determine how these peptides could be used safely in real-world treatments.

Enterobacter spp. and Giardia duodenalis are two resistant and globally distributed pathogens widely reported in humans and animals worldwide. To contrast the antimicrobial resistance phenomenon, this study aimed to evaluate the in vitro activity of antimicrobial peptides (AMPs), such as temporins, on the viability of Enterobacter spp. and G. duodenalis cysts isolated from naturally infected dogs. A total of 50 clinically healthy dogs were sampled, with 25 in each of the two sampling sessions. Rectal and oral swabs for Enterobacter spp. and fecal samples for G. duodenalis isolation were carried out. The AMPs were synthesized by a solid-phase peptide synthesis approach. Enterobacter ludwigii and E. hormaechei strains were isolated from two different dogs, while 16 dogs were positive for G. duodenalis. Subsequently, cysts and bacterial strains were treated with the following peptides: TL-34, TL-48, TL-42, TL-51, RB-71, and RB-58 at different concentrations (i.e., 250 mg/mL, 125 mg/mL, 62. mg/mL, and 31.25 for Enterobacter spp. strains and 0.15 mg/mL, 0.3 mg/mL, 0.6 mg/mL, and 1.2 mg/mL for G. duodenalis cysts). The results showed antimicrobial activity of TL-34, TL-48, and RB-71 against the two Enterobacter strains, while TL-51/TL-42 and RB-58 were not effective. In contrast, for G. duodenalis, TL-34, TL-48, TL-42, and RB-58 were effective at the two highest concentrations, inhibiting the viability of 100% of Giardia cysts, while the other two peptides (TL-51 and RB-71) showed less effectiveness. The AMPs used in this study have in vitro antimicrobial activity on cysts and bacterial strains and appear to have potential for the treatment of these infections in dogs.